The present invention relates to an offset printer, and more particularly, to a digital offset printer in which rotation of a drive motor is transmitted to a paper feed mechanism and a paper discharge mechanism through an impression cylinder, and also transmitted to an ink reciprocation roller through the impression cylinder, a blanket cylinder and a plate cylinder.
Japanese Patent Application Publication No. 9-510410 discloses an offset printer capable of performing offset printing with four different colors of inks. The printer includes a single impression cylinder, a single paper discharge mechanism, a single paper feed conveyer, a single transfer drum, two blanket cylinders, two plate cylinders and, ink rollers for the four colors. The paper feed conveyer and the transfer drum are adapted for delivering a paper to a surface of the impression cylinder. The paper is mounted on the surface of the impression cylinder. The paper discharge mechanism is adapted to discharge the paper from the impression cylinder. The blanket cylinder is pressed against the paper mounted on the impression cylinder.
The impression cylinder is rotated about its axis by the drive motor. Further, two blanket cylinders have their axes extending in a direction parallel with the axis of the impression cylinder, and the two blanket cylinders are in contact with the impression cylinder and are rotated upon rotation of the impression cylinder. The paper feed conveyer, the transfer drum and the paper discharge mechanism are also driven or rotated by the rotation of the impression cylinder.
Each plate cylinder has a peripheral surface provided with a thin plate where an image to be printed is formed. The two plate cylinders have their axes extending in a direction parallel with the axes of the blanket cylinders. Each plate cylinder is in contact with each blanket cylinder, and each plate cylinder is rotated upon rotation of each blanket cylinder. Each peripheral surface of the plate cylinder is divided into two segments. One of the segments is formed with an image with a single color, and remaining segment is formed with an image with a different color. Accordingly, the two plate cylinders form images of four colors.
The ink roller is adapted for supplying an ink to the plate of the plate cylinder. To this effect, two ink rollers are provided in contact with each plate cylinder so that two different colored inks can be supplied to each plate. Accordingly, totally four ink rollers are provided for four different colors. Axes of the ink rollers extend in parallel with the axis of the plate cylinder. The ink rollers are rotated upon rotation of the plate cylinder.
In the digital offset printer, the plate cylinders must be rotated about their axes so as to form images on the plates. This is similar to a laser printer in which a photo-sensitive drum is rotated so as to form an electro-static latent image on an outer peripheral surface of the drum. The drive motor, which is a single drive source, is driven to rotate the plate cylinder.